What is it like to paddle with a stick??

Cavitation
I think the noise IS cavitation. It takes energy, so try paddling without getting any noise. You’ll get a feeling of how much energy you need to apply.

Scratching noise…
I’ve heard this scratching a few times too, and thought to myself “So THAT’S what they (collective GP community) meant!”



I find that when I hear this, there is usually something wrong with my paddle. Sometimes I have a little lump of muddy clay stuck to the tip, once I had a piece of shell embedded in the tip, and sometimes the tips are just getting frayed and roughened. I’m sure ventilation can occur w/o any kind of damage as well if the stroke is “fighting” the water at all – plopping in and dragging air-- but on a paddle acceptably shaped, it’s rare once you develop a smooth stroke, in my experience, and usually caused by some kind of physical interference to smooth flow. So if you are hearing this and you don’t have any foreign crap stuck to your paddle or they’re not ragged, see if your edges are nicely rounded. I’ve seen GPs that still have a bit of squareness to the edges, they would be more susceptible to scratchy ventilation.






I think you’re correct
I did a rough Bernoulli equation calculation. Assuming water at 10 degree C and depth of 0.5 meter, the relative velocity between the paddle and the water would need to be about 14.5 meters/sec (47 ft/s or 32 mph) to get incipient cavitation.



I think it’s not unreasonable to assume you could get velocities this high within small turbulent eddies or vortices shed from a GP. If the GP was oriented a bit too cross-wise to the flow and pulled back sharply, cavitation would most likely occur at the sharpest edges of the paddle, say along the leading edge of the paddle near the tip. It would be interesting to verify this theory - cavitation can be hard to visualize, as the bubbles collapse so quickly.

Bernoulli???
You sure make paddling seem more complex than I need it to be. Does Bernoulli or whoever really matter?? Just paddle, have fun, and leave the equations for work or school!

Ventilation, not cavitation
Cavitation cannot occur with a paddle, but ventilation is very easy to induce with a GP. Some common causes are:


  • Reaching too far forward at the catch. This causes a reverse cant angle that traps water under the blade as it enters.


  • Pulling on the blade too soon. You have to wait until the blade is fully immersed before pulling on it with any real force.


  • Overpowering the paddle. If you pull too hard, you can draw air in around the blade.



    Typically, the cause of ventilation is a combination of these basic mistakes. It really just comes down to “unlearning” Euro techniques and learning proper GP techniques.

That doesn’t sound right
Cavitation is something that occurs with high-speed propellers, not kayak paddles. IIRC, the cause of cavitation is low pressure areas created by the motion of an object in the water. While a GP will produce some lift, it’s not a lot and I doubt it produces low enough pressures to come anywhere near causing cavitation.



Moreover, if you observe a GP blade in the water during a noisy stroke, there is always a telltale trail of bubbles leading down from the surface. The bubbles are air that’s been drawn down, not dissolved gasses released from the water.



Lastly, if cavitation could be caused by a kayak paddle, racers would never be able to get a clean stroke, as their paddle speeds and the lift that wing paddles generate are much higher than what a typical touring paddler ever produces.

That may be your hands
I find that my gloves or even the skin on my hands will squeak on the paddle after a while. Another possibility is that there’s a crack in the paddle and there is movement between the pieces as the paddle flexes.

d’oh
Hey, what can I tell you, my field is fluid mechanics and I do this stuff for fun. Remember, Bernoulli is your friend! But feel free to ignore my ramblings…

Cavitation vs ventilation

– Last Updated: May-25-10 1:52 PM EST –

I agree that ventilation is more likely. It might even explain nearly all of the noisy paddles we're talking about. But I wouldn't agree that cavitation is not possible. Cavitation is not caused by a solid body per se, but by high-speed fluid. If fluid moves from a high to low pressure region (as around the edge of a paddle), and it has to move around a sharp enough corner, its local velocity may briefly be high enough to cause cavitation.

It's easy to hear what cavitation sounds like - kink a garden hose with water flowing through it. As you reduce the cross-sectional area, you accelerate the fluid (by increasing the pressure gradient) and it will eventually start to cavitate, which you can hear pretty distinctly. The velocity of the water in the hose doesn't have to be very high; the constriction plus the sharp corner of the kink combine to cause it.

This doesn't prove anything, obviously, but I say 'never say never'. I hope to look into this issue someday soon.

Lots of rules

– Last Updated: May-25-10 2:09 PM EST –

Whenever I read these post with someone trying a GP, I would be quite discouraged with all the rules and doctrine. The GP is easier to use than a Euro Paddle. You don't have to cant or do anything different if you don't want to. You can just use it and the flutter will go away and nobody really knows why. I was using a GP before canting was invented or popularized by a Greenland Paddler who got popular around 8 years ago. (Maligiaq - Greenland National Champion) But before that, nobody knew anything and just used and enjoyed the GP without rules or special instructions.

When you convert from a euro, it does feel weird and a bit of a loss with bracing, but before you know it, you will like it and feel quite comfortable in all conditions with it. They don't grab the wind like a conventional blade and because you hold the blade for a lot of techniques, it makes rolling easier too. When I switch back over to a euro blade I now get flutter because I'm so use to the smooth easy stroke of the GP!

One last thing - you can sprint and accelerate from a dead stop just as fast as a euro too. It's a lot like a bicycle where you start out in a lower gear so your legs can move fast and not strain to get going.

Squeeky GPs
I have experienced this too. Not a function of gloves (don’t wear 'em) and paddle laminations are tight & sound.



I believe it is the result of micro-cavitation, air bubbles being liberated due to the vortices created in the stroke. Probably more noticeable in some designs, less so in others.



Seems to disappear when I clean up my technique.



Jim

Ventilation
This site describes the ventilation well:

http://www.guillemot-kayaks.com/guillemot/information/kayak_design/how_a_paddle_works



However, I get this strange noise even when the whole blade is submersed. I think you can create small cavitation bubbles (no air, just water vapour) at the tip of a paddle. Strange thing is that I don’t hear this with my euro blade.

paddle angle
So I found when I went out the other day an tried out my GP that it worked best when the top edge was tilted slightly back during the stroke. However, from what I’ve read, it sounds like it is supposed to be the other way around (top edge tilted forward). What IS the proper stroke angle for a GP?

Paddle Angle (forward or rearward)
You can do either! That’s the thing - you want some angle so that the paddle works like a wing (at an angle other than 90 degree instead of just dragging through the water perpendicular to the motion).



However, it is really better to start with a forward angle so that you can dip the paddle in the water quickly. Then if you need to, you can switch the angle through the stroke and finish with a rearward angle. This works quite well with a high-angle stroke that ends way far away from the hull (e.g. your hands move from close to the hull to away from the hull as your paddle stroke moves from dip to exit). This is how wing paddles are supposed to be used, except that you dip them straight or already canted back instead of forward - can’t do that rearward angle dipping with the GP effectively since the blade is too long and it will rob your stroke from power and time if you tried

forward tilt
I haven’t gone out yet and tried to paddle with a forward tilt yet, but when I tried it last year I found I had a difficult time keeping the paddle from running into the side of my kayak on the stroke. With the forward tilting blade the paddle wants to pull in towards the kayak, but if it is tilted back it has a tendency to pull away from the kayak, which is easier to control during the stroke. Perhaps it just takes practice as it appears that the forward tilting blade is obviously the more commonly accepted “proper” angle according to everything I’ve read about Maligiaq’s stroke technique.

Either
From a hydrodynamic standpoint, either forward or reverse cant angle will give a component of lift in the direction of travel, i.e. thrust, which is what’s generally desired.

Bubbles are drawn down with the blade
That’s why you’ll hear the “scratchy” sound even when the blade is fully submerged. If the water is clear, you will probably be able to see a trail of bubbles coming off the tip of the paddle. If you stop paddling when you hear it, you’ll see the bubbles rise to the surface.

GPs and Noise (a tad off topic)

– Last Updated: May-28-10 3:25 PM EST –

FWIW, one of the cool things I have observed with GPs is that they appear to act (at least my Cedar ones) as pretty effective hydrophones. That is, if I put one blade in the water and the other up to my ear, I hear all sorts of gurgles and burps and shrimps and so on.

The difference is…
…with a rearward cant, the paddle provides a bracing component, but you can’t pull on it very hard or it will skate on the surface. Other than when you’re actually doing a high brace or initiating a sculling stroke, I can’t think of any good reason to do this.



A forward cant causes the blade to submerge very quickly, which is desireable. The inward movement you experienced is to be expected, but if you resist it, the paddle produces much more bite on the water. It’s also normal to feel like the paddle is trying to capsize the kayak, but again, that feeling goes away as you get used to the stroke. It’s really a matter of learning how to pull on the canted paddle so you counterbalance the forces generated by the cant angle. You don’t need to angle the paddle forward very much to reap the benefits. I’ve heard heard 40-45 degrees mentioned, but that seems excessive to me. As the stoke progresses, the can’t angle naturally changes, typically increasing.



Just work with the paddle and see how it reacts to variations in technique. Over time, it will teach you how to use it.

yeah…wants to capsize me…
Just got back from playing around with my GP again today. Tried the forward tilt…not only does it want to drive itself into the side of my boat, but it also offers no support and feels like it is going to pull me over and capsize me. I tend to like the slight “bracing” component of tilting the paddle face back (like a euro paddle). As soon as I try to tilt it forward I feel all off balance.



Of course the salt in the wound is when I hand the paddle over to my wife and tell her what I am trying to do and she starts paddling down the lake without any problems looking like an Inuit paddler. Then she adds “I don’t know what you are having problems with…”



GRRRRRRR!!!